Continuous process of biogas purification and co-production of nano calcium carbonate in multistage membrane reactors

• Capture CO2 and synthesis nano CaCO3 at the same time.
• Two-stage cross flow membrane reactors with continuous operation mode were made.
• Produce gas with CO2 content lower than 3% and CaCO3 with 72.8 nm average particle size.
• The apparatus could run smoothly for at least 5 h.

CO2 capture is one of the key technologies in biogas production. Using lime slurry to purify biogas and co-production of nano calcium carbonate is an economical approach. In this work, multistage cross flow membrane reactors with continuous process were designed. Factors that influence CO2 absorption efficiency such as Ca(OH)2 slurry concentration, flow rate, additives, gas flow rate, membrane length and the connecting pipe length were studied to select the proper parameters. Results show that high slurry flow rate, low gas flow rate, long membrane and connecting pipe and the dosage of additives may enhance CO2 absorption, while Ca(OH)2 concentration has little impact on it. The hydrophobicity modification on the ceramic membrane using a silane coupling agent was also carried out. The change from hydrophilicity to hydrophobicity gave the reactor a higher mass transfer efficiency. Using the parameters carefully chosen based on the work above, the two-stage membrane reactors assembled successfully purified the gas (with end gas CO2 content lower than 3%) and produced nano calcium carbonate with 72.8 nm average particle size. Extension of the experiment showed that this apparatus could run smoothly for at least 5 h. This work may provide a new method in biogas purification and nano calcium carbonate synthesis.